Welding arc stabilization process

ABSTRACT

A system and method for stabilizing a welding arc is disclosed. The method of initiating the arc includes the steps of defining a wire feed speed based on a user selected wire feed speed and then abruptly reducing the wire feed speed before the wire feed speed reaches a relatively stabilized speed for welding, thereby allowing a welding arc to initiate and propagate to a generally steady state.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority to U.S.Ser. No. 10/710,593 filed Jul. 22, 2004, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to welding systems and, moreparticularly, to a welding system configured to automatically adjust awire feed speed to quickly and consistently generate stable weldingarcs.

During a welding process, a filler material, or wire, is typicallyintroduced to a workpiece. A power source generates an electrical signalthat results in an electrical potential between the workpiece and thefiller material when a separation is maintained therebetween. Thiselectrical potential generates an arc between the filler material andthe workpiece that then generates a weld pool. As the arc is initiated,if the filler material cannot support the electrical potential, asection of the filler material may collapse. Conversely, if theelectrical potential is insufficient to liquefy a portion of the fillermaterial to generate the weld pool, a short circuit condition candevelop between the filler material and the workpiece that will resultin the base of the arc as the filler material contacts the workpiece. Assuch, the parameters of the weld power signal and the rate of deliveryof filler material directly effect weld arc generation and the qualityof the starting arc.

Wire feeders are typically used to feed the filler material, generally ametal wire, into a weld during a welding process, such as Gas Metal ArcWelding (GMAW) or other welding processes. Typical wire feeders have adrive roller assembly for driving the metal feed from a feed spindlethrough a welding gun for introduction to the weld. Power is supplied tothe drive roller assembly by a welding power supply via a weld cable.The speed in which the metal filler material is fed to the weld is knownas the “wire feed speed” (WFS), and can be selected by an operator ofthe welding device who presets the WFS to a desired wire feed speed. Inother processes, the WFS can be adjusted to maintain a constantparameter, such as in constant voltage (CV) welding, constant current(CC) welding, or constant voltage-constant current (CV-CC) welding.Typically, the WFS is adjusted based on the thickness of the metal beingwelded, a wire deposition rate, a desired material transfer mode, anddesired weld power parameters such as a weld voltage or a weld current.The WFS is set to perform a desired welding application.

During a given welding process, if the welding arc is underpowered, theweld strength can be insufficient to adequately join the materials beingwelded. On the other hand, if the welding arc is overpowered, it ispossible to “burn through” the materials being welded. Between these twoextremes there is a range of power settings and wire feed speeds wherewelding can be performed, but may not have a preferred arccharacteristic. That is, if the power and feed speed result in aslightly underpowered welding arc, the welding process can repeatedlyarc and short as the wire touches the work piece resulting in aspattered weld. Alternatively, if the power and feed speed result in aslightly overpowered weld, the welding arc can repeatedly be formed andcollapse as extended sections of weld wire are prematurely introducedinto the weld, resulting in poor consistency. A weld produced witheither the overpowered or underpowered arc characteristics can havevarying degrees of poor weld quality in strength and/or aesthetics,inefficient power usage, and overall reduced operation efficiency.

Various known welding techniques have attempted to address the issue ofstable weld arc generation, or arc starts, with mixed results. One suchtechnique requires using a motor with retract capabilities, touching thewire to the workpiece, retracting to initiate an arc, and then feedingwire back into the weld after the start is completed. This techniquesubstantially increases system complexity by requiring a fast retractmotor and associated circuitry. It is also generally slower as itrequires substantial changes in both wire feed direction and repeatedwire feed speed accelerations and decelerations. Other techniquesprovide for adjusting the power, voltage, or current supplied to theweld from a power source during arc starts. These techniques monitorvoltage and/or current at the weld and adjust the amount of voltage orcurrent provided thereto in an attempt to better control the arccharacteristics. Other techniques provide a means for retracting thewire once an arc is detected. Because these systems directly control thepower signal provided to the weld, they must be relatively robust tosupport and manipulate the power signal required for welding processes.The robust nature of the control system increases assembly, repair, andmanufacture costs by requiring a device having additional components andcircuitry as well as increasing the overall complexity of the device.

It would, therefore, be desirable to have a system and method capable ofgenerating a stable welding arc that is relatively simple inconstruction and efficient in operation.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a system and method of generating astable initial welding arc that solves the aforementioned problems. Theinvention includes a welding system having a power source configured togenerate a power signal suitable for welding. A wire feeder is connectedto the power source and is configured to deliver a consumable electrodeto a weld. A controller automatically adjusts the wire feed speed duringinitial arc formation and allows the welding arc to fully propagateprior to the wire feed speed reaching a welding feed speed.

The present invention is particularly useful in systems that are capableof pulling the wire, as opposed to those that simply push the wire. Thisis so because systems that can pull wire generally have better controlover wire feed speed and acceleration and deceleration.

Therefore, in accordance with one aspect of the present invention, amethod of generating an initial welding arc is disclosed that includesthe steps of initiating wire feed speed, temporarily reducing wire feedspeed for a period of time based on detection of arc initialization, andthen adjusting wire feed speed based on a user selected speed.

According to another aspect of the present invention, a method ofestablishing a welding arc is disclosed that includes defining a wirefeed speed based on a user selected wire feed speed and then reducingthe wire feed speed before the wire feed speed reaches the user selectedwire feed speed at weld stabilization.

In accordance with yet a further aspect of the present invention, awelding system is disclosed having a power source configured to generatea power signal suitable for welding. A wire feeder is connected to thepower source and is configured to deliver a consumable wire electrode toa weld at a wire feed speed. A controller is connected to the wirefeeder and is configured to automatically set a rate of acceleration ofthe wire feed speed, then abruptly reduce the wire feed speed beforewelding arc stabilization and then set the wire feed speed to arelatively stable speed for welding.

According to another aspect of the present invention, a welding systemis disclosed that includes a power source configured to generate a powersignal suitable for welding-type applications. A wire feeder isconstructed to deliver a filler material to a weld. The welding systemincludes means for controlling a filler material delivery rate thatreduces the delivery rate based on welding arc initialization prior toarc stabilization.

Various other features, objects and advantages of the present inventionwill be made apparent from the following detailed description and thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a perspective view of a welding system.

FIG. 2 is a sectional view of the wire feeder taken along lines 2-2 ofFIG. 1.

FIG. 3 is a front elevational view of a control panel of the wire feederillustrated in FIG. 1.

FIG. 4 is a flow chart setting forth the steps of a control algorithmcarried out by a controller for allowing generation of stable welding.

FIG. 5 is a graphical representation of voltage versus time showing theoperation of the control algorithm shown in FIG. 4.

FIG. 6 is a graphical representation of voltage versus time showing analternate operation of the control algorithm shown in FIG. 4.

FIG. 7 shows another torch for use with the welding system shown in FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a welding-type system 10 is shown according to thepresent invention. System 10 includes a power source 12, which can be anAC or a DC welding power supply operable in a constant current (CC), aconstant voltage (CV), or a combination thereof. In one embodiment, anexhaust 13 extends from power source 12 and vents exhaust gas from aninternal combustion engine of the power source. It is understood thatpower source 12 could also be configured to be powered by a generator ora power grid. The power source 12 has a work cable 14 and clamp 16designed to hold a workpiece 18 for welding. Power source 12 isconnected to a wire feeder 20 via cable 22. Although shown as being aseparately connected component, it is understood that wire feeder 20could be physically attached to, or incorporated into, and/or internalto, power source 12. A weld cable 22 is connected between the powersource 12 and the wire feeder 20. The wire feeder 20, which in oneembodiment is portable, also includes a welding gun or torch 24, and anoptional arc sensing lead 26 configured to provide arc conditionfeedback from workpiece 18 to the wire feeder 20 and/or the power source12. It is understood that an optional arc sensing lead 26 could beintegrated into work cable 14 connecting clamp 16 to power source 12and/or integrated into cable 25 attaching torch 24 to wire feeder 20 toprovide weld torch feedback. A shielding gas cylinder 28 is alsoconnected to the wire feeder 20 to provide shielding gas for the weldingprocess in a known manner.

When the welding torch 24 is positioned proximate to workpiece 18,welding wire is fed into contact with the workpiece 18. Once triggered,an electrical current and voltage are generated between the welding wireand the workpiece that causes the welding wire to be heated and melt. Anelectrical arc is established which causes the welding wire to continueto melt as well as transfer the melted welding wire to the workpiece 18where the welding wire fuses with the workpiece 18. Because theelectrical energy supplied to the welding system is typically greaterthan that required to melt the welding wire, most of the remainingenergy is in the form of heat which is transferred to the surface of theworkpiece 18 resulting in the workpiece 18 also melting to create fusionbetween two workpieces and between the melted welding wire and theworkpiece(s) 18. As the welding torch 24 is translated across theworkpiece 18, melted welding wire is continuously transferred to theworkpiece 18. The wire feeder is designed to introduce flux cored, solidsteel, stainless steel, or aluminum welding wire to a weld. One skilledin the art will appreciate that this technique and these materials areillustrative only, and that the present invention is equivalentlyapplicable with other welding systems having different operatingspecifications.

Referring now to FIG. 2, the wire feeder 20 includes a wire driveassembly 30 to drive feed wire from a spool 32 designed to supportwelding wire (not shown) that is supplied to the weld under control of acontroller 34 embodied in operational circuitry secured to a circuitboard (not shown) that is connected to the power source 12 through cord22 and cord 21, as shown in FIG. 1. Alternatively, controller 34 may beincorporated into the power source 12. The controller is governed by amicroprocessor capable of being programmed to operate according tocertain algorithms and/or programs. User selections or inputs receivedby the controller from a display and control panel, as shown in FIG. 3,and an internally programmed algorithm cause welding system 10 tooperate according to the user selections. Controller 34 has a detectioncircuit 35 that is connected to the arc sensing lead 26 and configuredto detect and communicate characteristics of the welding arc tocontroller 34. Wire feeder 20 is generally referred to as a push-typewire feeder in that the feed wire is “pushed” to the torch. While thepresent invention is applicable in such push wire feeders, it isparticularly advantageous with pull-type wire feeders, as shown in FIG.7, wherein the feed wire is pulled from a source to the torch.Additionally, there are circumstances, such as when the torch is locatedan extended distance from a wire spool, when it is desirable to bothpush and pull the feed wire to the torch in unison. Such systems arereferred to as push-pull type wire feed systems.

Referring now to FIG. 3, a front elevational view of a control panel ofa wire feeder is illustrated. Control panel 36 is designed to allow theuser to input various welding parameters so as to define the weldingprocess to be carried out. Specifically, the control panel includes anON/OFF switch 38 that allows the user to switch the wire feeder on oroff. Control panel 36 also includes a JOG/PURGE button or switch 40 thatallows the user to purge or remove existing gas from the wire feeder.That is, controller 34, shown in FIG. 2, detects activation of purgebutton 40 of FIG. 3, and in response thereto, transmits a control signalto the gas valve assembly of the wire feeder to cause the drive assemblyto purge any residual gas from the wire feeder. Control panel 36 canalso include a JOG button that when selected causes controller 34 totransmit a jog command to the drive assembly to step the wireadvancement in defined increments.

Control panel 36 also provides a user interface on the wire feeder thatallows the user to set a target voltage via control knob 42, as well asa wire feed speed control knob 44. One skilled in the art willappreciate that the functionality achieved with dual knobs 42 and 44 mayalso be achieved with a single telescoping knob or with the analog ordigital switches. Additionally, it is further understood that ratherthan setting a target voltage, control knob 42 could be configured toprovide a target current. As will be described in greater detail below,the wire feed controller will regulate the drive assembly such that thewire feed speed selected by the user via adjusting control knob 44 isautomatically adjusted by controller 34 to facilitate smooth andrepeatable generation of a relatively stable welding arc. That is, thecontroller will automatically adjust the wire feed speed so that arelatively stable initial arc is generated independent of the wire feedspeed selected by the user. It should be noted, in one embodiment, thata legend 46 associated with voltage adjustment control knob 42represents a scaled voltage level of the desired target voltage. Thatis, user adjustment of control knob 42 to reference numeral 2 of legend46 represents that the user desires the target voltage to be 20V in onecase.

Control panel 36 illustrated in FIG. 3 represents an example of acontrol panel which may be incorporated in the wire feeder. One skilledin the art will readily appreciate that the appearance and/ororientation of the selector switches, knobs, buttons, and the like maydiffer from that specifically illustrated. Additionally, LCDs and LEDs(not shown) may also be utilized and are considered within the scope ofthe present invention. For example, control panel 36 may be constructedsuch that an LCD displays one or more menus that allow the user tointeractively set the target arc voltage as well as the initial wirefeed speed. In this regard, the user may navigate through a series ofmenus or windows that are displayed on the LCD in defining theoperational parameters of the welding process to be carried out.

As noted above, the present invention provides a controller that isconfigured to automatically adjust the wire feed speed at which theconsumable electrode is delivered to a weld so that a welding arc isconsistently and repeatedly generated with an arc initialization tostabilize the welding process more quickly, efficiently, and withoutoperator intervention. Referring now to FIG. 4, a preferred controltechnique or algorithm 50 for automatically adjusting the wire feedspeed is illustrated. The preferred technique or process 50 begins atstep 52 with a user setting a constant current (CC) level or a constantvoltage (CV) level depending on the welding process desired. Theoperator can also set a desired wire feed speed on a control menu on thewire feeder such as that illustrated in FIG. 3, or it may be set basedon the welding process desired. The controller will then acquire thedesired wire feed speed 54 and determine and set a wire speed run-invalue. The wire speed run-in value is often less than, but not limitedto, the user selected desired wire feed speed. The controller will thentransmit a control signal to the drive assembly of the wire feeder suchthat wire is fed to the weld at a speed equal to the run-in value.

Eventually, as wire is delivered to a desired weld area at the run-inspeed, a short circuit or initial arc is detected 56. If no arc has beenformed, control technique 50 continues to attempt to detect an initialarc condition 58 until the initial arc is generated. After detection ofan initial arc 56, controller 34 automatically adjusts the feed speed 60to allow the arc to propagate from the initial arc to a sustainable,relatively stable, weld arc. After the initial arc has been detected,the wire speed is preferably adjusted to a minimum value, which can bezero, for a duration of time as determined by the desired wire feedspeed. Optionally, rather than specify the duration of the minimum wirefeed speed value, control algorithm 50 could continue to monitor the arccondition 62 until a stable weld arc is formed 64. After the duration oftime with the wire speed adjusted to the minimum value, and havingthereby formed a relatively stable welding arc between the feed wire anda workpiece, control algorithm 50 adjusts the wire feed speed 66 to theuser selected desired feed speed for the duration of the weldingoperation. Having established a generally stable welding arc, controlalgorithm 50 ends at 68 and is configured to repeat with the nextinitial arc generation.

FIG. 5 shows the generation of a stable arc condition when the torch isinitiated in an open circuit condition with a work piece. An opencircuit voltage 70 is initiated at torch trigger activation. A delay 72is maintained between the torch trigger activation and the wire feedspeed 73, which is increased to a run-in rate 74 to ensure sufficientarcing at the site of the welding application. It is understood that theramps shown in the wire feed speed in FIGS. 5 and 6 are representativeof component lag and that the wire feed speed command is essentially astep function and is therefore nearly instantaneous. Delay 72 ispreferably approximately 20 ms but, understandably, could be modifiedfor a particular welding application. When the feed wire touches thework piece, a short circuit voltage 76 is detected that initiates adetectable arc 78 between the workpiece and the wire. Upon detection ofthe initial arc 78, wire feed speed 73 is abruptly reduced to a minimumwire speed 80. Minimum wire speed 80 is less than a user selected wirefeed rate 82 and is maintained for a delay period 84 determined in partby the user selected wire feed speed. It is understood that minimum wirespeed 80 could approach zero with a corresponding reduction in theduration of delay period 84. Preferably, delay period 84 is maintainedfor approximately 50 ms at which time wire feed speed 73 is allowed tothen achieve the user selected wire feed rate 82. By abruptly reducingwire feed rate 73 after the detection of an initial arc 78, a preferredgap is achieved and a relatively stable arc condition is generated.

Comparatively, FIG. 6 shows the generation of a stable welding arc whenan initial short circuit condition exists between the welding wire andthe workpiece, such as when the two are in very close proximity orcontact. Wire feed 86 is delayed a duration 88 to allow generation of anarc. A power source delivers a welding-power signal to the weld and aninitial arc 90 is generated during delay duration 88 which isapproximately 20 ms. Understandably, initial arc 90 could be formedanytime during delay duration 88 when the electrical potential betweenthe weld wire and the work piece reaches a value capable of melting thewire and then generating an electrical arc between the wire and theworkpiece. After delay duration 88, wire feed 86 is increased to arun-in speed 92. Having detected an initial arc 90, wire feed 86 reducesto a minimum wire feed speed value 94 for a duration 96. The duration 96that wire feed 86 is maintained at the minimum wire feed speed value 94is determined in part by the user specified wire feed speed. Afterduration 96 has transpired, wire feed speed 86 is allowed to achieve theuser selected wire feed speed 98 and maintains a desired arc power 100.

Regardless whether a welding process is initiated from an open circuitcondition or a short circuit condition between the weld wire and theworkpiece, controller 34 maintains the weld wire feed speed after theinitial arc generation at a speed that maintains and allows a weldingarc to form. The speed with which the weld wire is introduced to theweld maintains a desirable gap distance between the work piece and theweld wire as the welding arc is formed. By maintaining a gap distancethat can be electrically arced over during arc formation, a weldingdevice is provided that allows for repeated and efficient weld arcformation.

As previously discussed, FIG. 7 shows a torch 102 that can be preferablyimplemented with the present invention in addition to, or as analternative to, torch 24. Torch 102 includes housings 104, 106 enclosinga motor. The motor is configured to pull a consumable wire 108. Themotor drives paired alignment rollers within the housings 104, 106 todrive the wire from opposite sides of the wire to substantially equalizethe driving forces applied to the wire 108. Such a wire driving means isgenerally referred to as a pull-type wire feeder in that it pulls thewire from a feeder to the torch. It is understood that torch 102 couldbe combined with wire feeder 24 shown in FIG. 2 to achieve a push/pullwire feed system. Regardless of the wire feed system applied, bymanipulating the rate and period of introduction of weld wire to a weldpoint, the present invention forms a relatively stable weld arc in arepeatable and economical manner.

Therefore, one embodiment of the present invention has a method ofstabilizing a welding arc comprising the steps of initiating wire feedspeed, temporarily reducing wire feed speed for a period of time basedon detection of arc initialization, and adjusting wire feed speed basedon a user selected speed.

Another embodiment of the present invention includes a method ofestablishing a welding arc comprising defining a wire feed speed basedon a user selected wire feed speed and reducing the wire feed speedbefore the wire feed speed reaches the user selected wire feed at weldstabilization.

A further embodiment of the present invention includes a welding systemhaving a power source configured to generate a power signal suitable forwelding. The welding system includes a wire feeder configured to delivera consumable wire electrode to a weld at a wire feed speed. A controlleris connected to the wire feeder and is configured to automatically set arate of acceleration of the wire feed speed, then abruptly reduce thewire feed speed before welding arc stabilization and then set the wirefeed speed to a relatively stable speed for welding.

Another embodiment of the present invention has a welding system thatincludes a power source configured to generate a power signal suitablefor welding-type applications. A wire feeder constructed to deliver afiller material to a weld is connected to the power source. The weldingsystem includes means for controlling a filler material delivery ratebased on welding arc initialization prior to arc stabilization.

As one skilled in the art will fully appreciate, the heretoforedescription of welding devices is applicable to all weld systems withwirefeed requirements. Reference to welding power, welding-type power,or welders generally, includes welding, cutting, or heating power.Description of a welding apparatus illustrates just one embodiment inwhich the present invention may be implemented.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A method of generating a welding arc comprising the steps of:initiating wire feed speed; temporarily reducing wire feed speed for aperiod of time based on detection of arc initialization and a userselected speed; and adjusting wire feed speed based on the user selectedspeed.
 2. The method of claim 1 wherein the step of initiating wire feedspeed is further defined as initiating wire feed speed at a run-in valueand wherein the period of time is determined by the user selected speed.3. The method of claim 2 wherein the period of time is 50 ms.
 4. Themethod of claim 1 further comprising the step of detectinginitialization of a welding arc.
 5. The method of claim 4 furthercomprising the step of delaying a wire drive power until aftergeneration of a welding power signal by a power source.
 6. The method ofclaim 5 wherein a duration of the delay is less than approximately 20ms.
 7. The method of claim 1 further comprising initiating a powersource power signal and initiating a wire feeder power signal by atrigger.
 8. The method of claim 1 further comprising at least one of thesteps of pulling wire from a spool to a torch, pushing and pulling wireto a torch, and pushing wire to a torch.
 9. A welding system comprising:a power source configured to generate a power signal suitable forwelding; a wire feeder connected to the power source and configured todeliver a consumable wire electrode to a weld at a wire feed speed; anda controller connected to the wire feeder and configured to: define thewire feed speed based on a user selected wire feed speed; reduce thewire feed speed before the wire feed speed reaches the user selectedwire feed at weld stabilization; and automatically adjust the wire feedspeed to the user selected wire feed speed after a predeterminedduration of time after weld stabilization.
 10. The welding system ofclaim 9 wherein the controller is further configured to reduce the wirefeed speed based on arc initialization.
 11. The welding system of claim9 wherein the controller is further configured to determine a durationof the reduced wire feed speed based on the user selected wire feedspeed.
 12. The welding system of claim 9 further comprising generating aweld power prior to powering a wire feeder.
 13. The welding system ofclaim 9 wherein the wired feeder is configured to perform at least oneof pulling wire from a wire spool to a torch, pushing and pulling wireto a torch, and pushing wire to a torch.
 14. The welding system of claim9 wherein the controller is further configured to reduce the wire feedspeed to approximately zero between an initial run-in speed and reachingthe user selected wire feed speed.
 15. A welding system comprising: apower source configured to generate a power signal suitable forwelding-type applications; a wire feeder constructed to deliver a fillermaterial to a weld; and means for controlling a filler material deliveryrate that reduces the delivery rate without reversing a deliverydirection based on welding arc initialization prior to arcstabilization.
 16. The system of claim 15 further comprising means fordetecting arc condition.
 17. The system of claim 16 wherein thedetecting means detects an initial arc condition and a stable arccondition.
 18. The system of claim 15 wherein the controlling meansinstructs a delivery rate of a user defined wire feed speed afterwelding arc stabilization.
 19. The system of claim 15 wherein thecontrolling means reduces the delivery rate for a predetermined amountof time prior to arc stabilization.
 20. The system of claim 15 whereinthe controlling means comprises a programmable microprocessor.